Nonwoven fibrous webs and methods of making and using thereof

ABSTRACT

Disclosed herein are nonwoven fibrous web comprising a population of fibers, wherein the fibers are formed from a composite that comprises: (i) a thermoplastic elastomeric polymer (TPE) component; (ii) a soft elastomeric polymer component that at ambient temperatures is above its glass transition temperature; and (iii) optionally a filler. Also described are methods of making these nonwoven fibrous webs as well as articles made therefrom.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. Provisional Application No.63/027,118, filed May 19, 2020, which is hereby incorporated herein byreference in its entirety.

BACKGROUND

Nonwoven fibrous webs have been used to produce absorbent or adsorbentarticles useful, for example, as absorbent wipes for surface cleaning,as gas adsorbents and liquid absorbents, as fluid filtration media, andas absorptive barrier materials for use as an acoustic or thermalinsulation. Nonwoven fibrous webs can be formed by a variety oftechniques including carding, garneting, air-laying, wet-laying, meltblowing, spunbonding, electrospinning, and stitch bonding. Furtherprocessing of a nonwoven can be used to add properties such as strength,durability, and texture. Examples of further processing includecalendering, hydroentangling, needle tacking, resin bonding,thermo-bonding, ultrasonic welding, embossing, and laminating.

While many nonwovens with varied characteristics have been prepared,there remains a need for improved nonwoven materials. In particular,there is a need for new nonwoven materials suitable for use in thepreparation of personal protective equipment including facemasks.

SUMMARY

Provided herein nonwoven fibrous web comprising a population of fibers,wherein the fibers are formed from a composite that comprises: (i) athermoplastic elastomeric polymer (TPE) component; (ii) a softelastomeric polymer component that at ambient temperatures is above itsglass transition temperature; and (iii) optionally a filler.

The TPE component can comprise a block copolymer having at least oneelastomeric block. For example, the TPE component can comprise apolystyrene-polyisobutylene block copolymer, polystyrene-polybutadieneblock copolymer, polystyrene-polyisoprene block copolymer,polystyrene-poly(ethylene-butylene block copolymer,polystyrene-poly(ethylene-propylene) block copolymer, a thermoplasticpolyolefin (TPO), a dynamically vulcanized TPV, or a blend or copolymerthereof. In certain embodiments, the TPE component can comprise apolyisobutylene-based TPE, such aspolystyrene-polyisobutylene-polystyrene (SIBS). The TPE component canhave any suitable structure, such as a linear, star, arborescent, comb,brush, centipede, hyperbranched, or dendritic structure. In someembodiments, the TPE component can comprises a linear block copolymer,such as a linear triblock polystyrene-polyisobutylene-polystyrenecopolymer (L_SIBS).

The soft elastomeric polymer component can comprise, for example,polyisobutylene, a polyisobutylene-isoprene copolymer, apolyisobutylene-styrene copolymer, polyisobutylene-alkyl styrenecopolymers, halogenated polyisobutylene-alkyl styrene terpolymers,polybutadiene, polyisoprene, polyethylene-propylene copolymers,polyethylene-propylene diene terpolymers, and combinations thereof. Incertain embodiments, the soft elastomeric polymer component can comprisepolyisobutylene, a polyisobutylene-isoprene copolymer (e.g., butylrubber), or any combination thereof. As with the TPE component, the softelastomeric polymer component can have any suitable structure, such as alinear, star, arborescent, comb, brush, centipede, hyperbranched, ordendritic structure.

In some embodiments, the TPE can be present in an amount from about 10%to about 90% by weight of the composite, and the soft elastomericpolymer component can be present in an amount from about 90 to about 10%by weight of the composite, based on the total weight of the composite.In certain embodiments, the TPE can be present in an amount from about40% to about 60% by weight of the composite, and the soft elastomericpolymer component can be present in an amount from about 60 to about 40%by weight of the composite, based on the total weight of the composite.

The filler can comprise any suitable filler material. In someembodiments, the filler can comprise an antimicrobial filler. Theantimicrobial filler can be an inorganic material that comprises onemore antimicrobial metals (e.g., silver, copper, zinc, and combinationsthereof). In some examples, the antimicrobial filler can comprise zincoxide, carbon black, or any combination thereof. In some embodiments,the filler can be present in an amount from about 2% to about 40% byweight of the composite, such as from about 5% to about 30% by weight,based on the total weight of the composite.

The population of fibers comprises population of fine fibers, apopulation of microfibers, a population of ultrafine microfibers, apopulation of sub-micrometer fibers, or any combination thereof.

In some embodiments, the nonwoven fibrous web can be formed as a singlelayer. In some embodiments, the nonwoven web can have a basis weight ofat least 80 g/m², such as a basis weight of at least 100 g/m², at least150 g/m², or at least 200 g/m². In certain embodiments, the nonwoven webcan be self-supporting. The nonwoven fibrous web can be hydrophobic. Insome embodiments, the nonwoven fibrous web can exhibit a water contactangle of at least 120°, as determined by goineometry.

In some embodiments, the nonwoven web can exhibit an average filtrationefficiency relative to 20 nm to 450 nm NaCl particles of at least 60%,as measured using the U.S. NIOSH (National Institute for OccupationalSafety and Health) N95 Filtering Facepiece Respirator (FFR)certification method. In some embodiments, the nonwoven web can exhibitan average filtration efficiency relative to 300 nm NaCl particles of atleast 50%, measured using the U.S. NIOSH (National Institute forOccupational Safety and Health) N95 Filtering Facepiece Respirator (FFR)certification method.

The nonwoven fibrous webs described herein can be used to construct avariety of articles, including gas filtration articles, liquidfiltration articles, sound absorption articles, surface cleaningarticles, cellular growth support articles, drug delivery articles,personal hygiene articles, and wound dressing articles. In someembodiments, the nonwoven fibrous webs described herein can be fashionedinto facemasks.

Also provided are methods of making fibrous nonwoven webs. These methodscan comprise forming a plurality of fibers from a composite comprising:(i) a thermoplastic elastomeric polymer (TPE) component; (ii) a softelastomeric polymer component that at ambient temperatures is above itsglass transition temperature; and (iii) optionally a filler; andcollecting at least a portion of the fibers to form a nonwoven web. Insome embodiments, the methods can further comprises combining (e.g.,melt processing) the TPE component, the soft elastomeric polymercomponent, and the filler to form the composite.

The web can be formed using any suitable method, such as a melt-blowing,spun-bonding, or melt-spinning process. In some examples, the web can beformed using melt-spinning, filament extrusion, electrospinning, gas jetfibrillation or combinations thereof. Optionally, methods can furthercomprise post heating the web, for example, by controlled heating orcooling of the web.

DESCRIPTION OF DRAWINGS

FIG. 1A shows the multilayer design of conventional surgical masks. Asshown in FIG. 1A, conventional surgical masks employ a trilayer designthat includes an outer (often polypropylene) spunbond nonwoven layer, acentral (often polypropylene) meltblown layer which serves as theprimary filter material, and an inner spunbond layer.

FIG. 1B shows the multilayer design of a conventional N95 mask. As shownin FIG. 1B, these masks include multiple meltblown nonwoven layersdisposed between an inner and outer needle punched cotton layer.

FIG. 2A is a photograph showing a nonwoven web formed by electrospinningFormulation 2.

FIG. 2B is an electron micrograph of a nonwoven web formed byelectrospinning Formulation 2.

FIG. 3A is a photograph showing a nonwoven web formed by electrospinningFormulation 1.

FIG. 3B is an electron micrograph of a nonwoven web formed byelectrospinning Formulation 1.

FIG. 4 is a plot showing the filtration efficiency (in %, as measuredusing the NIOSH N95 Filtering Facepiece Respirator (FFR) certificationmethod) of five example PIB-based nonwoven webs as a function ofpressure drop (in Pa).

FIG. 5 illustrates the measurement of the water contact angle of anexample nonwoven web using goniometry.

FIG. 6 illustrates an example facemask fabricated using aself-supporting nonwoven web prepared herein.

FIG. 7 schematically illustrates the structure of various polymerarchitectures.

DETAILED DESCRIPTION Definitions

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. Methods and materials aredescribed herein for use in the present invention; other, suitablemethods and materials known in the art can also be used. The materials,methods, and examples are illustrative only and not intended to belimiting. All publications, patent applications, patents, sequences,database entries, and other references mentioned herein are incorporatedby reference in their entirety. In case of conflict, the presentspecification, including definitions, will control.

“Nonwoven fibrous web” means an article or sheet having a structure ofindividual fibers or filaments, which are interlaid, but not in anidentifiable manner as in a knitted fabric. Nonwoven fabrics or webshave been formed from many processes such as for example, meltblowingprocesses, spunbonding processes, and bonded carded web processes.

“Cohesive nonwoven fibrous web” means a fibrous web characterized byentanglement or bonding of the fibers sufficient to form aself-supporting web.

“Web” as used herein is a network of entangled fibers forming a sheetlike or fabric like structure.

“Self-supporting” means a web having sufficient coherency and strengthso as to be drapable and handleable without substantial tearing orrupture.

“Meltblowing” and “meltblown process” means a method for forming anonwoven fibrous web by extruding a molten fiber-forming materialthrough a plurality of orifices to form filaments while contacting thefilaments with air or other attenuating fluid to attenuate the filamentsinto fibers, and thereafter collecting the attenuated fibers. Anexemplary meltblowing process is taught in, for example, U.S. Pat. No.6,607,624 (Berrigan et al.).

“Meltblown fibers” means fibers prepared by a meltblowing or meltblownprocess.

“Spunbonding” and “spun bond process” mean a method for forming anonwoven fibrous web by extruding molten fiber-forming material ascontinuous or semi-continuous filaments from a plurality of finecapillaries of a spinneret, and thereafter collecting the attenuatedfibers. An exemplary spunbonding process is disclosed in, for example,U.S. Pat. No. 3,802,817 (Matsuki et al.).

“Spun bond fibers” and “spunbonded fibers” mean fibers made usingspunbonding or a spun bond process. Such fibers are generally continuousfilaments and are entangled or point bonded sufficiently to form acohesive nonwoven fibrous web such that it is usually not possible toremove one complete spun bond fiber from a mass of such fibers. Thefibers may also have shapes such as those described, for example, inU.S. Pat. No. 5,277,976 (Hogle et al.), which describes fibers withunconventional shapes.

“Carding” and “carding process” mean a method of forming a nonwovenfibrous web webs by processing staple fibers through a combing orcarding unit, which separates or breaks apart and aligns the staplefibers in the machine direction to form a generally machine directionoriented fibrous nonwoven web. An exemplary carding process is taughtin, for example, U.S. Pat. No. 5,114,787 (Chaplin et al.).

“Bonded carded web” refers to nonwoven fibrous web formed by a cardingprocess wherein at least a portion of the fibers are bonded together bymethods that include for example, thermal point bonding, autogenousbonding, hot air bonding, ultrasonic bonding, needle punching,calendering, application of a spray adhesive, and the like.

“Autogenous bonding” means bonding between fibers at an elevatedtemperature as obtained in an oven or with a through-air bonder withoutapplication of solid contact pressure such as in point-bonding orcalendering.

“Calendering” means a process of passing a nonwoven fibrous web throughrollers with application of pressure to obtain a compressed and bondedfibrous nonwoven web. The rollers may optionally be heated.

“Densification” means a process whereby fibers which have been depositedeither directly or indirectly onto a filter winding arbor or mandrel arecompressed, either before or after the deposition, and made to form anarea, generally or locally, of lower porosity, whether by design or asan artifact of some process of handling the forming or formed filter.Densification also includes the process of calendering webs.

“Air-laying” is a process by which a nonwoven fibrous web layer can beformed. In the air-laying process, bundles of small fibers havingtypical lengths ranging from about 3 to about 52 millimeters (mm) areseparated and entrained in an air supply and then deposited onto aforming screen, usually with the assistance of a vacuum supply. Therandomly deposited fibers may then be bonded to one another using, forexample, thermal point bonding, autogenous bonding, hot air bonding,needle punching, calendering, a spray adhesive, and the like. Anexemplary air-laying process is taught in, for example, U.S. Pat. No.4,640,810 (Laursen et al.).

“Wet-laying” is a process by which a nonwoven fibrous web layer can beformed. In the wet-laying process, bundles of small fibers havingtypical lengths ranging from about 3 to about 52 millimeters (mm) areseparated and entrained in a liquid supply and then deposited onto aforming screen, usually with the assistance of a vacuum supply. Water istypically the preferred liquid. The randomly deposited fibers may byfurther entangled (e.g., hydro-entangled), or may be bonded to oneanother using, for example, thermal point bonding, autogeneous bonding,hot air bonding, ultrasonic bonding, needle punching, calendering,application of a spray adhesive, and the like. An exemplary wet-layingand bonding process is taught in, for example, U.S. Pat. No. 5,167,765(Nielsen et al.). Exemplary bonding processes are also disclosed in, forexample, U.S. Patent Application Publication No. 2008/0038976 A1(Berrigan et al.).

To “co-form” or a “co-forming process” means a process in which at leastone fiber layer is formed substantially simultaneously with or in-linewith formation of at least one different fiber layer. Webs produced by aco-forming process are generally referred to as “co-formed webs.”

“Die” means a processing assembly for use in polymer melt processing andfiber extrusion processes, including but not limited to meltblowing andthe spunbonding process.

“Particulate” and “particle” are used substantially interchangeably.Generally, a particulate or particle means a small distinct piece orindividual part of a material in finely divided form. However, aparticulate may also include a collection of individual particlesassociated or clustered together in finely divided form. Thus,individual particulates used in certain exemplary embodiments of thepresent disclosure may clump, physically intermesh, electro-staticallyassociate, or otherwise associate to form particulates.

The term “median fiber diameter” means fiber diameter determined byproducing one or more images of the fiber structure, such as by using ascanning electron microscope; measuring the fiber diameter of clearlyvisible fibers in the one or more images resulting in a total number offiber diameters, x; and calculating the median fiber diameter of the xfiber diameters. Typically, x is greater than about 20, more preferablygreater than about 50, and desirably ranges from about 50 to about 200.

“Effective Fiber Diameter” or “EFD” is the apparent diameter of thefibers in a fiber web based on an air permeation test in which air at 1atmosphere and room temperature is passed through a web sample at aspecified thickness and face velocity (typically 5.3 cm/sec), and thecorresponding pressure drop is measured. Based on the measured pressuredrop, the Effective Fiber Diameter is calculated as set forth in Davies,C. N., The Separation of Airborne Dust and Particulates, Institution ofMechanical Engineers, London Proceedings, 1B (1952).

The term “fine fiber” generally refers to fibers having a median fiberdiameter of no greater than about 50 micrometers (μm), preferably nogreater than 25 μm, more preferably no greater than 20 μm, still morepreferably no greater than 15 μm, even more preferably no greater than10 μm, and most preferably no greater than 5 μm.

“Microfibers” are a population of fibers having a median fiber diameterof at least one μm but no greater than 100 μm.

“Ultrafine microfibers” are a population of microfibers having a medianfiber diameter of two μm or less.

“Sub-micrometer fibers” are a population of fibers having a median fiberdiameter of no greater than one μm.

When reference is made herein to a batch, group, array, etc. of aparticular kind of microfiber, e.g., “an array of sub-micrometerfibers,” it means the complete population of microfibers in that array,or the complete population of a single batch of microfibers, and notonly that portion of the array or batch that is of sub-micrometerdimensions.

“Continuous oriented microfibers” means essentially continuous fibersissuing from a die and traveling through a processing station in whichthe fibers are permanently drawn and at least portions of the polymermolecules within the fibers are permanently oriented into alignment withthe longitudinal axis of the fibers (“oriented” as used with respect tofibers means that at least portions of the polymer molecules of thefibers are aligned along the longitudinal axis of the fibers).

“Separately prepared microfibers” means a stream of microfibers producedfrom a microfiber-forming apparatus (e.g., a die) positioned such thatthe microfiber stream is initially spatially separate (e.g., over adistance of about 1 inch (25 mm) or more from, but will merge in flightand disperse into, a stream of larger size microfibers.

“Solidity” is a nonwoven web property inversely related to density andcharacteristic of web permeability and porosity (low Soliditycorresponds to high permeability and high porosity), and is defined bythe equation:

${{Solidity}(\%)} = \frac{\left\lbrack {3.937*{Web}{Basis}{Weight}\left( {g/m^{2}} \right)} \right\rbrack}{\left\lbrack {{Web}{Thickness}({mils})*{Bulk}{Density}\left( {g/{cm}^{3}} \right)} \right\rbrack}$

“Web basis weight” is calculated from the weight of a 10 cm×10 cm websample, and is usually expressed in grams per square meter (gsm).

“Web thickness” is measured on a 10 cm×10 cm web sample using athickness testing gauge having a tester foot with dimensions of 5cm×12.5 cm at an applied pressure of 150 Pa.

“Bulk density” is the mass per unit volume of the bulk polymer orpolymer blend that makes up the web, taken from the literature.

“Molecularly same” polymer means polymers that have essentially the samerepeating molecular unit, but which may differ in molecular weight,method of manufacture, commercial form, and the like.

“Fluid treatment unit,” “fluid filtration article,” or “fluid filtrationsystem” means an article containing a fluid filtration medium, such as aporous nonwoven fibrous web. These articles typically include a filterhousing for a fluid filtration medium and an outlet to pass treatedfluid away from the filter housing in an appropriate manner. The term“fluid filtration system” also includes any related method of separatingraw fluid, such as untreated gas or liquid, from treated fluid.

“Void volume” means a percentage or fractional value for the unfilledspace within a porous body such as a web or filter, which may becalculated by measuring the weight and volume of a filter, thencomparing the filter weight to the theoretical weight of a solid mass ofthe same constituent material of that same volume.

“Porosity” means a measure of void spaces in a material. Size,frequency, number, and/or interconnectivity of pores and voidscontribute the porosity of a material.

“Layer” means a single stratum formed between two major surfaces. Alayer may exist internally within a single web, e.g., a single stratumformed with multiple strata in a single web have first and second majorsurfaces defining the thickness of the web. A layer may also exist in acomposite article comprising multiple webs, e.g., a single stratum in afirst web having first and second major surfaces defining the thicknessof the web, when that web is overlaid or underlaid by a second webhaving first and second major surfaces defining the thickness of thesecond web, in which case each of the first and second webs forms atleast one layer. In addition, layers may simultaneously exist within asingle web and between that web and one or more other webs, each webforming a layer.

“Adjoining” with reference to a particular first layer means joined withor attached to another, second layer, in a position wherein the firstand second layers are either next to (i.e., adjacent to) and directlycontacting each other, or contiguous with each other but not in directcontact (i.e., there are one or more additional layers interveningbetween the first and second layers).

As used herein, the term “soft elastomeric polymer” means a polymer thatat ambient temperatures is above its glass transition temperature. Inother words, this material is one which at ambient temperatures is aviscous material having an amorphous structure. It is this component ofthe polymer matrix which is primarily responsible for the softness andhigh damping characteristics of the final composite.

As used herein, the term “thermoplastic elastomeric polymer (TPE)” meansa thermoplastic polymer that at ambient temperatures exhibits a suitabledegree of resilience and/or softness, but provides a thermolabilephysical network so that the shape retention properties of the finalpolymer matrix are increased compared with those properties of the softelastomeric polymer component alone. It is the thermoplastic nature ofthis second thermoplastic polymer component of the matrix of thecomposite which is primarily responsible for the shape retention and/orlow compression creep properties of the final composite.

As used herein, the term “linear architecture” means a linear polymerchain.

As used herein, the term “star architecture” means a polymer having acore from which a number of arms (3-infinite or as many as possible tofill the space) emanate.

As used herein, the term “arborescent architecture” means a randomlybranched structure resembling a tree (branches on branches).

As used herein, the term “comb architecture” means a linear polymerchain to which a number of shorter linear chains are attached, with thestructure resembling a comb.

IIR is a commercial butyl elastomer, and SIBS is a commercial lineartriblock polystyrene-polyisobutylene-polystyrene thermoplasticelastomer.

SBS means polystyrene-polybutadiene block copolymers.

SIS means polystyrene-polyisoprene block copolymers

SEBS and SEPS means the hydrogenated versions of SBS and SIS.

SEBS means polystyrene-poly(ethylene-butylene)-polystyrene.

SEPS means polystyrene-poly(ethylene-propylene)-polystyrene.

TPO means thermoplastic polyolefins.

TPV means dynamically vulcanized TPVs.

The above listed soft elastomer components and thermoplastic elastomercomponents can have various architectures (linear, star, arborescent,comb. etc).

Fibers and Nonwoven Fibrous Webs

Provided herein nonwoven fibrous web comprising a population of fibers,wherein the fibers are formed from a composite that comprises: (i) athermoplastic elastomeric polymer (TPE) component; (ii) a softelastomeric polymer component that at ambient temperatures is above itsglass transition temperature; and (iii) optionally a filler.

The population of fibers comprises population of fine fibers, apopulation of microfibers, a population of ultrafine microfibers, apopulation of sub-micrometer fibers, or any combination thereof.

In some embodiments, the nonwoven fibrous web can be formed as a singlelayer. In some embodiments, the nonwoven web can have a basis weight ofat least 80 g/m², such as a basis weight of at least 100 g/m², at least150 g/m², or at least 200 g/m². In certain embodiments, the nonwoven webcan be self-supporting. The nonwoven fibrous web can be hydrophobic. Insome embodiments, the nonwoven fibrous web can exhibit a water contactangle of at least 120° (e.g., at least 125°, at least 130°, or at least135°), as determined by goineometry.

In some embodiments, the nonwoven web can exhibit an average filtrationefficiency relative to 20 nm to 450 nm NaCl particles of at least 50%(e.g., at least 55%, at least 60%, at least 65%, at least 70%, at least75%, at least 80%, at least 85%, at least 90%, or at least 95%), asmeasured using the U.S. NIOSH (National Institute for OccupationalSafety and Health) N95 Filtering Facepiece Respirator (FFR)certification method. In some embodiments, the nonwoven web can exhibitan average filtration efficiency relative to 300 nm NaCl particles of atleast 50% (e.g., at least 55%, at least 60%, at least 65%, at least 70%,at least 75%, at least 80%, at least 85%, at least 90%, or at least95%), as measured using the U.S. NIOSH (National Institute forOccupational Safety and Health) N95 Filtering Facepiece Respirator (FFR)certification method.

The components of the composite are described in more detail below.

Thermoplastic Elastomeric Polymer (TPE) Components

A variety of suitable TPE components can be incorporated in thecomposites described herein. Examples of suitable TPEs includethermoplastic polyurethanes (TPU), styrenic block copolymers (TPS(TPE-s)), thermoplastic polyolefinelastomers (TPO (TPE-o)),thermoplastic vulcanizates (TPV (TPE-v or TPV)), thermoplasticcopolyesters (TPC (TPE-E)), thermoplastic polyamides (TPA (TPE-A)), andcopolymers and blends thereof. The TPE component can have any suitablestructure, such as a linear, star, arborescent, comb, brush, centipede,hyperbranched, or dendritic structure.

In some embodiments, the TPE component can comprise a block copolymerhaving at least one elastomeric block. For example, the TPE componentcan comprise a polystyrene-polyisobutylene block copolymer,polystyrene-polybutadiene block copolymer, polystyrene-polyisopreneblock copolymer, polystyrene-poly(ethylene-butylene block copolymer,polystyrene-poly(ethylene-propylene) block copolymer, a thermoplasticpolyolefin (TPO), a dynamically vulcanized TPV, or a blend or copolymerthereof.

In certain embodiments, the TPE component can comprise apolyisobutylene-based TPE (i.e., a block copolymer having at least oneelastomeric polyisobutylene block). Examples of suchpolyisobutylene-based TPEs includepolystyrene-polyisobutylene-polystyrene (SIBS). Linear triblock SIBSTPEs were introduced commercially in 2003 by Kaneka Co. of Japan. SuchTPEs are described, for example, in U.S. Pat. Nos. 4,946,899 and4,946,899, each of which is hereby incorporated herein by reference inits entirety. Star-branched SIBS were subsequently developed, andconsidered the second generation with improved properties. The thirdgeneration, arborescent (dendritic, tree-like) SIBS TPEs were introducedin 2002. Such TPEs are described, for example, in U.S. Pat. Nos.6,747,098 and 8,748,530, each of which is hereby incorporated herein byreference in its entirety. A fourth generation of PIB-based TPEs(poly(alloocimene-isobutylene-alloocimene) or AIBA for short) have alsobeen developed. Such TPEs are described, for example, in U.S. Pat. No.9,790,301, which is hereby incorporated herein by reference in itsentirety. Any of these polyisobutylene-based TPEs are suitable.

In some embodiments, the TPE component can comprise a linearpolyisobutylene TPE, a star polyisobutylene TPE, or an arborescentpolyisobutylene TPE.

In certain embodiments, the TPE component can comprise a linearpolyisobutylene TPE that comprises an elastomeric midblock ofpolyisobutylene with a number average molecular weight of from about10,000 to about 200,000 and a molecular weight distribution of fromabout 1.05 to about 1.6 and two plastomeric endblocks of at least onepolymerized C8 to C12 monovinylidene aromatic monomer which may bear atleast one C1 to C4 alkyl substituent or a bromine or chlorine atom onthe aromatic ring comprising from about 5 to about 50 weight percent ofa total of 100 weight percent of the linear triblock copolymer. Inspecific embodiments, the TPE component can comprise a linearpolyisobutylene TPE that comprises an elastomeric midblock ofpolyisobutylene having a number average molecular weight of from about35,000 to about 100,000 and a molecular weight distribution of fromabout 1.05 to about 1.6 and two plastomeric endbocks of polystyrenecomprising from about 5 to about 50 weight percent of a total of 100weight percent of the linear triblock copolymer.

In certain embodiments, the TPE component can comprise a star-shapedpolyisobutylene TPE that comprises from three to six arms that compriseinner elastomeric blocks of polyisobutylene with a number averagemolecular weight of from about 10,000 to about 200,000 and outerplastomeric blocks of at least one polymerized C8 to C12 monovinylidenearomatic monomer which may bear at least one C1 to C4 alkyl substituentor a bromine or chlorine atom on the aromatic ring comprising from about10 to about 55 weight percent of a total of 100 weight percent of thestar-shaped block copolymer. In specific embodiments, the TPE componentcan comprise a star-shaped polyisobutylene TPE that comprises three armsthat comprise inner elastomeric blocks of polyisobutylene with a numberaverage molecular weight of from about 35,000 to about 100,000 and outerplastomeric blocks of polystyrene comprising from about 10 to about 55weight percent of a total of 100 weight percent of the star-shaped blockcopolymer.

In some embodiments, the TPE component can comprise a linearpolyisobutylene TPE, a star polyisobutylene TPE, an arborescentpolyisobutylene TPE, a linearpoly(isobutylene(OH)-b-(isobutylene-co-para-methylstyrene), a starpoly(isobutylene(OH)-b-(isobutylene-co-para-methylstyrene), anarborescent poly(isobutylene(OH)-b-(isobutylene-co-para-methylstyrene),a linear poly(styrene-b-isobutylene-b-styrene), a starpoly(styrene-b-isobutylene-b-styrene), an arborescentpoly(styrene-b-isobutylene-b-styrene), a linearpoly(isobutylene-OH-co-para-methylstyrene), a starpoly(isobutylene-OH-co-para-methyl styrene), an arborescentpoly(isobutylene-OH-co-para-methylstyrene), a linearpoly(alloocimene-b-isobutylene-b-alloocimene), a starpoly(alloocimene-b-isobutylene-b-alloocimene), or an arborescentpoly(alloocimene-b-isobutylene-b-alloocimene). In one example, the TPEcomponent can comprise an arborescent PIB-based TPE withpoly(para-methylstyrene) end blocks (arbPIB-MS). In certain embodiments,the TPE component can comprises a linear triblockpolystyrene-polyisobutylene-polystyrene copolymer (L_SIBS).

In some embodiments, the TPE component can be present in the compositein an amount of at least about 10% by weight (e.g., at least about 15%by weight, at least about 20% by weight, at least about 25% by weight,at least about 30% by weight, at least about 35% by weight, at leastabout 40% by weight, at least about 45% by weight, at least about 50% byweight, at least about 55% by weight, at least about 60% by weight, atleast about 75% by weight, at least about 80% by weight, or at leastabout 85% by weight), based on the total weight of the composite. Insome embodiments, the TPE component can be present in the composite inan amount of about 90% by weight or less (e.g., about 85% by weight orless, about 80% by weight or less, about 75% by weight or less, about70% by weight or less, about 65% by weight or less, about 60% by weightor less, about 55% by weight or less, about 50% by weight or less, about45% by weight or less, about 40% by weight or less, about 35% by weightor less, about 30% by weight or less, about 25% by weight or less, about20% by weight or less, or about 15% by weight or less), based on thetotal weight of the composite.

The TPE component can be present in the component in an amount rangingfrom any of the minimum values described above to any of the maximumvalues described above. For example, in some embodiments, the TPEcomponent can be present in an amount from about 10% to about 90% byweight (e.g., from about 25% to about 90% by weight, from about 30% toabout 65% by weight, or from about 40% to about 60% by weight), based onthe total weight of the composite.

In one example, the composite can comprise a blend of butyl elastomersand block copolymers of polyisobutylene, such as the blends described inU.S. Pat. No. 5,276,094, which is hereby incorporated herein byreference in its entirety.

Soft Elastomeric Polymer Components

Suitable polymers for use as the soft elastomeric polymer componentinclude polyisobutylene, polyisobutylene-isoprene copolymers,polyisobutylene-styrene copolymers, polyisobutylene-alkyl styrenecopolymers, halogenated polyisobutylene-alkyl styrene terpolymers,polybutadiene, polyisoprene, polyethylene-propylene copolymers,polyethylene-propylene diene terpolymers. Polyisobutylene,polyisobutylene-isoprene copolymers, particularly preferred. Selectionof an optimum polymer may depend upon the exact mechanical propertiesrequired of it, which may depend to at least some extent on the amountof it to be incorporated in the composite and the relative physicalproperties of soft elastomeric polymer component and the TPE component,and possibly any other components of the composite which are present,including the filler.

In some embodiments, the soft elastomeric polymer component can comprisepolyisobutylene, a polyisobutylene-isoprene copolymer, apolyisobutylene-styrene copolymer, polyisobutylene-alkyl styrenecopolymers, halogenated polyisobutylene-alkyl styrene terpolymers,polybutadiene, polyisoprene, polyethylene-propylene copolymers,polyethylene-propylene diene terpolymers, and combinations thereof. Incertain embodiments, the soft elastomeric polymer component can comprisepolyisobutylene, a polyisobutylene-isoprene copolymer, or anycombination thereof.

In certain embodiments, the soft elastomeric polymer component cancomprise a butyl rubber. Butyl rubber is well known in the art and is apolymer of a C4 to C6 isoolefin, preferably isobutylene, and a C4 to C8conjugated diolefin, preferably isoprene. A preferred butyl polymercontains from about 97 to 99.5 weight percent of isobutylene and fromabout 0.5 to about 3 weight percent of isoprene. Butyl rubber typicallyhas a molecular weight expressed as the Mooney (ML1+8 at 125° C.), offrom about 25 to about 65, preferably from about 40 to about 60.

In some embodiments, the soft elastomeric polymer component can bepresent in the composite in an amount of at least about 10% by weight(e.g., at least about 15% by weight, at least about 20% by weight, atleast about 25% by weight, at least about 30% by weight, at least about35% by weight, at least about 40% by weight, at least about 45% byweight, at least about 50% by weight, at least about 55% by weight, atleast about 60% by weight, at least about 75% by weight, at least about80% by weight, or at least about 85% by weight), based on the totalweight of the composite. In some embodiments, the soft elastomericpolymer component can be present in the composite in an amount of about90% by weight or less (e.g., about 85% by weight or less, about 80% byweight or less, about 75% by weight or less, about 70% by weight orless, about 65% by weight or less, about 60% by weight or less, about55% by weight or less, about 50% by weight or less, about 45% by weightor less, about 40% by weight or less, about 35% by weight or less, about30% by weight or less, about 25% by weight or less, about 20% by weightor less, or about 15% by weight or less), based on the total weight ofthe composite.

The soft elastomeric polymer component can be present in the componentin an amount ranging from any of the minimum values described above toany of the maximum values described above. For example, in someembodiments, the soft elastomeric polymer component can be present in anamount from about 10% to about 90% by weight (e.g., from about 25% toabout 90% by weight, from about 30% to about 65% by weight, or fromabout 40% to about 60% by weight), based on the total weight of thecomposite.

Fillers

The filler, when present, can comprise any suitable filler material.Examples of fillers include precipitated hydrated silica, clay, talc,asbestos, glass fibers, aramid fibers, mica, calcium metasilicate, zincsulfate, barium sulfate, zinc sulfide, lithopone, silicates, siliconcarbide, diatomaceous earth, polyvinyl chloride, carbonates (e.g.,calcium carbonate, zinc carbonate, barium carbonate, and magnesiumcarbonate), metals (e.g., titanium, tungsten, aluminum, bismuth, nickel,molybdenum, iron, lead, copper, boron, cobalt, beryllium, zinc, andtin), metal alloys (e.g., steel, brass, bronze, boron carbide whiskers,and tungsten carbide whiskers), oxides (e.g., zinc oxide, tin oxide,iron oxide, calcium oxide, aluminum oxide, titanium dioxide, magnesiumoxide, and zirconium oxide), particulate carbonaceous materials (e.g.,graphite, carbon black, cotton flock, natural bitumen, cellulose flock,and leather fiber), microballoons (e.g., glass and ceramic), fly ash,regrind (i.e., core material that is ground and recycled), nanofillersand combinations thereof.

In some embodiments, the filler can comprise an antimicrobial filler.The antimicrobial filler can be an inorganic material that comprises onemore antimicrobial metals (e.g., silver, copper, zinc, and combinationsthereof). In some examples, the antimicrobial filler can comprise zincoxide, carbon black, or any combination thereof.

In some embodiments, the filler can be present in the composite in anamount of at least about 2% by weight (e.g., at least about 5% byweight, at least about 10% by weight, at least about 15% by weight, atleast about 20% by weight, at least about 25% by weight, at least about30% by weight, or at least about 35% by weight), based on the totalweight of the composite. In some embodiments, the filler can be presentin the composite in an amount of about 40% by weight or less (e.g.,about 35% by weight or less, about 30% by weight or less, about 25% byweight or less, about 20% by weight or less, about 15% by weight orless, about 10% by weight or less, or about 5% by weight or less), basedon the total weight of the composite.

The filler can be present in the component in an amount ranging from anyof the minimum values described above to any of the maximum valuesdescribed above. For example, in some embodiments, the filler can bepresent in an amount from about 2% to about 40% by weight (e.g., fromabout 2% to about 30% by weight, from about 5% to about 30% by weight,from about 5% to about 25% by weight, or from about 5% to about 20% byweight), based on the total weight of the composite.

Other Additives

The composite can optionally include one or more additional additives.Typically, the amount of additives other than the TPE component, softelastomeric polymer component, and filler is no greater than about 25%by weight, desirably, no greater than about 10% by weight, or no greaterthan 5% by weight, based on the total weight of the composite. Suitableadditives include, but are not limited to, stabilizers, plasticizers,tackifiers, flow control agents, cure rate retarders, adhesion promoters(for example, silanes and titanates), adjuvants, impact modifiers,expandable microspheres, thermally conductive particles, electricallyconductive particles, colorants such as dyes and/or pigments,antioxidants, optical brighteners, antimicrobial agents, surfactants,wetting agents, fire retardants, and repellents such as hydrocarbonwaxes, silicones, fluorochemicals, antistatic agents, odor controlagents, perfumes and fragrances, combinations thereof, and the like.

One or more of the above-described additives may be used to reduce theweight and/or cost of the resulting fiber and layer, adjust viscosity,or modify the thermal properties of the fiber or confer a range ofphysical properties derived from the physical property activity of theadditive including electrical, optical, density-related, liquid barrieror adhesive tack related properties.

In some embodiments, the composite can further comprise a plasticizer.In some cases, the plasticizer can comprise poly(ethylene glycol),oligomeric polyesters, fatty acid monoesters and di-esters, citrateesters, glycols such glycerin; propylene glycol, polyethoxylatedphenols, mono or polysubstituted polyethylene glycols, higher alkylsubstituted N-alkyl pyrrolidones, sulfonamides, triglycerides, citrateesters, esters of tartaric acid, benzoate esters, polyethylene glycolsand ethylene oxide propylene oxide random and block copolymers having amolecular weight no greater than 10,000 Daltons (Da), preferably nogreater than about 5,000 Da, more preferably no greater than about 2,500Da; and combinations thereof.

In some embodiments, the composite can further comprise an antimicrobialagent (other than the filler described above). The antimicrobial agentmay be added to impart antimicrobial activity to the fibers. Theantimicrobial agent is the component that provides at least part of theantimicrobial activity, i.e., it has at least some antimicrobialactivity for at least one microorganism. In some exemplary embodiments,a suitable antimicrobial agent may be selected from a fatty acidmonoester, a fatty acid di-ester, an organic acid, a silver compound, aquaternary ammonium compound, a cationic (co)polymer, an iodinecompound, or combinations thereof. Other examples of antimicrobialinclude those described in U.S. Patent Application Publication No.2008/0142023, which is hereby incorporated by reference herein in itsentirety.

Surface Treatment of Webs

The nonwoven fibrous webs described herein may be rendered morerepellent by treatment with numerous compounds. For example, thenonwovens may be subjected to post web forming surface treatments whichinclude paraffin waxes, fatty acids, bee's wax, silicones,fluorochemicals and combinations thereof. For example, the repellentfinishes may be applied as disclosed in U.S. Pat. Nos. 5,027,803;6,960,642; and 7,199,197, all of which are incorporated by referenceherein in its entirety. Repellent finishes may also be melt additivessuch as those described in U.S. Pat. No. 6,262,180, which isincorporated by reference herein in its entirety.

Preferred fluorochemicals comprise a perfluoroalkyl group having atleast 4 carbon atoms. These fluorochemicals may be small molecules,oligamers, or polymers. Silicone fluid repellents also may be suitable.In some instances hydrocarbon-type repellents may also be suitable.

Classes of fluorochemical agents or compositions useful in thisinvention include compounds and polymers containing one or morefluoroaliphatic radicals, Rf. In general, fluorochemical agents orcompositions useful as a repellent additive comprise fluorochemicalcompounds or polymers containing fluoroaliphatic radicals or groups, Rf.The fluoroaliphatic radical, Rf, is a fluorinated, stable, inert,non-polar, preferably saturated, monovalent moiety which is bothhydrophobic and oleophobic. It can be straight chain, branched chain,or, if sufficiently large, cyclic, or combinations thereof, such asalkylcycloaliphatic radicals. The skeletal chain in the fluoroaliphaticradical can include catenary divalent oxygen atoms and/or trivalentnitrogen atoms bonded only to carbon atoms. Generally Rf will have 3 to20 carbon atoms, preferably 6 to about 12 carbon atoms, and will containabout 40 to 78 weight percent, preferably 50 to 78 weight percent,carbon-bound fluorine. The terminal portion of the Rf group has at leastone trifluoromethyl group, and preferably has a terminal group of atleast three fully fluorinated carbon atoms, e.g., CF₃CF₂CF₂—. Thepreferred Rf groups are fully or substantially fluorinated, as in thecase where Rf is perfluroalkyl, CnF₂n+1-.

Examples of such compounds include, for example, fluorochemicalurethanes, ureas, esters, amines (and salts thereof), amides, acids (andsalts thereof), carbodiimides, guanidines, allophanates, biurets, andcompounds containing two or more of these groups, as well as blends ofthese compounds.

Useful fluorochemical polymers containing Rf radicals include copolymersof fluorochemical acrylate and/or methacrylate monomers withco-polymerizable monomers, including fluorine-containing andfluorine-free monomers, such as methyl methacrylate, butyl acrylate,octadecyl methacrylate, acrylate and methacrylate esters ofpoly(oxyalkylene) polyol oligomers and polymers, e.g., poly(oxyethylene)glycol dimethacrylate, glycidyl methacrylate, ethylene, vinyl acetate,vinyl chloride, vinylidene chloride, vinylidene fluoride, acrylonitrile,vinyl chloroacetate, isoprene, chloroprene, styrene, butadiene,vinylpyridine, vinyl alkyl esters, vinyl alkyl ketones, acrylic andmethacrylic acid, 2-hydroxyethyl acrylate, N-methylolacrylamide,2-(N,N,N-trimethylammonium)ethyl methacrylate and the like.

The relative amounts of various comonomers which can be used with thefluorochemical monomer will generally be selected empirically, and willdepend on the substrate to be treated, the properties desire from thefluorochemical treatment, i.e., the degree of oil and/or waterrepellency desired, and the mode of application to the substrate.

Useful fluorochemical agents or compositions include blends of thevarious classes of fluorochemical compounds and/or polymers describedabove. Also, blends of these fluorochemical compounds or polymers withfluorine-free compounds, e.g., N-acyl aziridines, or fluorine-freepolymers, e.g., polyacrylates such as poly(methyl methacrylate) andpoly(methyl methacrylate-co-decyl acrylate), polysiloxanes and the like.

The fluorochemical agents or compositions can include non-interferingadjuvants such as wetting agents, emulsifiers, solvents (aqueous andorganic), dyes, biocides, fillers, catalysts, curing agents and thelike. The final fluorochemical agent or composition should contain, on asolids basis, at least about 5 weight percent, preferably at least about10 weight percent carbon-bound fluorine in the form of said Rf groups inorder to impart the benefits described in this invention. Suchfluorochemicals are generally known and commercially available asperfluoroaliphatic group bearing water/oil repellent agents whichcontain at least 5 percent by weight of fluorine, preferably 7 to 12percent of fluorine in the available formulations.

By the reaction of the perfluoroaliphatic thioglycols withdiisocyanates, there results perfluoroaliphatic group-bearingpolyurethanes. These products are normally applied in aqueous dispersionfor fiber treatment. Such reaction products are described in U.S. Pat.No. 4,054,592, incorporated herein by reference.

Another group of suitable compounds are perfluoroaliphatic group-bearingN-methylol condensation products. These compounds are described in U.S.Pat. No. 4,477,498, incorporated herein by reference where theemulsification of such products is dealt with in detail.

The perfluoroaliphatic group-bearing polycarbodimides are, e.g.,obtained by reaction of perfluoroaliphatic sulfonamide alkanols withpolyisocyanates in the presence of suitable catalysts. This class ofcompounds can be used by itself, but often is used with other Rf-groupbearing compounds, especially with (co)polymers. Thus, another group ofcompounds which can be used in dispersions is mentioned. Among thesecompounds all known polymers bearing fluoroaliphatic residues can beused, also condensation polymers, such as polyesters and polyamideswhich contain the corresponding perfluoroaliphatic groups, areconsidered but especially (co)polymers on the basis of e.g. Rf-acrylatesand Rf-methacrylates, which can contain different fluorine-free vinylcompounds as comonomers. In DE-A 2 310 801, these compounds arediscussed in detail. The manufacture of Rf-group bearingpolycarbodimides as well as the combination of these compounds with eachother is also described in detail.

Besides the aforementioned perfluoroaliphatic group-bearing agents,further fluorochemical components may be used, for example,Rf-group-bearing guanidines, U.S. Pat. No. 4,540,479, Rf-group-bearingallophanates, U.S. Pat. No. 4,606,737 and Rf-group-bearing biurets, U.S.Pat. No. 4,668,406, the disclosures which are incorporated herein byreference. These classes are mostly used in combination. Others includefluoroalkyl-substituted siloxanes, e.g., CF₃(CF₂)₆CH₂O(CH₂)₃Si(OC₂H₅)₃—.

The useful compounds show, in general, one or more perfluoroaliphaticresidues with preferably at least 4 carbon atoms, especially 4 to 14atoms each. An exemplary fluorochemical is a formulation of 70% solventsand 30% emulsified solid fluorochemical polymers. The formulationincludes as solvents 11% methyl isobutyl ketone, 6% ethylene glycol and53% water. The fluorochemical polymers are a 50/50 blend of 5/95copolymer of butyl acrylate and C₈F₁₇SO₂(CH₃)C₂H₄O—CCH═CH₂ prepared asdescribed in U.S. Pat. No. 3,816,229, incorporated herein by reference(see especially column 3, lines 66-68 and column 4, lines 1-11) for a10/90 copolymer. The second component of the 50/50 blend is a copolymerprepared from 1 mole of a tri-functional phenyl isocyanate (availablefrom Upjohn Company under the name PAPI), 2 moles ofC₈F₁₇N(CH₂CH₃)CH₂CH₂OH and 1 mole of stearyl alcohol prepared asdescribed in U.S. Pat. No. 4,401,780, incorporated herein by reference(see especially Table 1, C2 under footnote A). Emulsifiers used areconventional commercially available materials such as polyethoxylatedquaternary ammonium compounds (available under the name 5% Ethoquad18/25 from Akzo Chemie America) and 7.5% of a 50/50 mixture ofC₈F₁₇SO₂NHC₃H₆N(CH₃)₃Cl and a polyethoxylated sorbitan monooleate(available from ICI Limited under the name TWEEN 80). Suchfluorochemicals are non-yellowing and particularly non-irritating to theskin as well as providing articles that are stable having excellent longterm aging properties. Exemplary fluorochemicals are available under thetrade designations SCOTCHGARD, SCOTCH-RELEASE, and 3M BRAND TEXTILECHEMICAL and are commercially from the 3M Company. Other commerciallyavailable materials include materials that use fluorotelomer chemistrymaterials provided by DuPont (available from duPont deNemours andCompany, Wilmington, Del.).

Suitable silicones for use to obtain the low surface energy layers ofthe instant invention include any of the silicones known to thoseskilled in the art to provide water repellency and optionally oilrepellency to fibers and films. Silicone fluids typically consist oflinear polymers of rather low molecular weight, namely about4000-25,000. Most commonly the polymers are polydimethylsiloxanes.

For use as fluids with enhanced thermal stability, silicones containingboth methyl and phenyl groups are often used. Generally, the phenylgroups make up 10-45% of the total number of substituent groups present.Such silicones are generally obtained by hydrolysis of mixtures ofmethyl- and phenylchlorosilanes. Fluids for use in textile treatment mayincorporate reactive groups so that they may be cross-linked to give apermanent finish. Commonly, these fluids contain Si—H bonds (introducedby including methyldichlorosilane in the polymerization system) andcross-linking occurs on heating with alkali.

Examples of suitable silicones are those available from Dow-CorningCorporation such as C2-0563 and from General Electric Corporation suchas GE-SS4098. Especially preferred silicone finishes are disclosed inU.S. Pat. No. 5,045,387.

Methods of Forming Fibers and Webs

Also provided are methods of making fibrous nonwoven webs. These methodscan comprise forming a plurality of fibers from a composite comprising:(i) a thermoplastic elastomeric polymer (TPE) component; (ii) a softelastomeric polymer component that at ambient temperatures is above itsglass transition temperature; and (iii) optionally a filler; andcollecting at least a portion of the fibers to form a nonwoven web.

In some embodiments, the methods can further comprises combining (e.g.,melt processing) the TPE component, the soft elastomeric polymercomponent, and the filler (when present) to form the composite. Thecomposite may be manufactured by conventional methods well known inpolymer technology, as are well known to the person skilled in the artand well described in the literature. For example, the TPE component,the soft elastomeric polymer component, and the filler (when present)can be combined in a standard type of mixer until a completelyhomogeneous matrix is formed, optionally with further heating ifnecessary. Then the composite may be cooled and passed to the nextprocessing stage, which is preferably fiber formation. Alternatively,the composite can be formed into pellets, etc. which can be stored andsubsequently processed into fibers.

Any suitable method of fiber formation may be used, such as amelt-blowing, spun-bonding, or melt-spinning process. The population offibers comprises population of fine fibers, a population of microfibers,a population of ultrafine microfibers, a population of sub-micrometerfibers, or any combination thereof. Suitable methods of fiber formationcan be selected, for example, based on the desired fiber dimensions. [Insome examples, the web can be formed using melt-spinning, filamentextrusion, electrospinning, gas jet fibrillation or combinationsthereof.

In some embodiments, the nonwoven fibrous webs may include fine fibersthat are substantially sub-micrometer fibers, fine fibers that aresubstantially microfibers, or combinations thereof. In some embodiments,a nonwoven fibrous web may be formed of sub-micrometer fibers commingledwith coarser microfibers providing a support structure for thesub-micrometer nonwoven fibers. The support structure may provide theresiliency and strength to hold the fine sub-micrometer fibers in thepreferred low solidity form. The support structure could be made from anumber of different components, either singly or in concert. Examples ofsupporting components include, for example, microfibers, discontinuousoriented fibers, natural fibers, foamed porous cellular materials, andcontinuous or discontinuous non oriented fibers.

Sub-micrometer fibers are typically very long, though they are generallyregarded as discontinuous. Their long lengths—with a length-to-diameterratio approaching infinity in contrast to the finite lengths of staplefibers—causes them to be better held within the matrix of microfibers.They are usually organic and polymeric and often of the molecularly samepolymer as the microfibers. As the streams of sub-micrometer fiber andmicrofibers merge, the sub-micrometer fibers become dispersed among themicrofibers. A rather uniform mixture may be obtained, especially in thex-y dimensions, or plane of the web, with the distribution in the zdimension being controlled by particular process steps such as controlof the distance, the angle, and the mass and velocity of the mergingstreams.

The relative amount of sub-micrometer fibers to microfibers included ina nonwoven fibrous web can be varied depending on the intended use ofthe web. An effective amount, i.e., an amount effective to accomplishdesired performance, need not be large in weight amount. Usually themicrofibers account for at least one weight percent and no greater thanabout 75 weight percent of the fibers of the web. Because of the highsurface area of the microfibers, a small weight amount may accomplishdesired performance. In the case of webs that include very smallmicrofibers, the microfibers generally account for at least 5 percent ofthe fibrous surface area of the web, and more typically 10 or 20 percentor more of the fibrous surface area.

In one exemplary embodiment, a microfiber stream is formed and asub-micrometer fiber stream is separately formed and added to themicrofiber stream to form the nonwoven fibrous web. In another exemplaryembodiment, a sub-micrometer fiber stream is formed and a microfiberstream is separately formed and added to the sub-micrometer fiber streamto form the nonwoven fibrous web. In these exemplary embodiments, eitherone or both of the sub-micrometer fiber stream and the microfiber streamis oriented. In an additional embodiment, an oriented sub-micrometerfiber stream is formed and discontinuous microfibers are added to thesub-micrometer fiber stream, e.g. using a process as described in U.S.Pat. No. 4,118,531 (Hauser).

In some exemplary embodiments, the method of making nonwoven fibrous webcomprises combining the sub-micrometer fiber population and themicrofiber population into a nonwoven fibrous web by mixing fiberstreams, hydroentangling, wet forming, plexifilament formation, or acombination thereof. In combining the sub-micrometer fiber populationwith the microfiber population, multiple streams of one or both types offibers may be used, and the streams may be combined in any order. Inthis manner, nonwoven composite fibrous webs may be formed exhibitingvarious desired concentration gradients and/or layered structures.

For example, in certain exemplary embodiments, the population ofsub-micrometer fibers may be combined with the population of microfibersto form an inhomogenous mixture of fibers. In other exemplaryembodiments, the population of sub-micrometer fibers may be formed as anoverlayer on an underlayer comprising the population of microfibers. Incertain other exemplary embodiments, the population of microfibers maybe formed as an overlayer on an underlayer comprising the population ofsub-micrometer fibers

In other exemplary embodiments, the nonwoven fibrous article may beformed by depositing the population of sub-micrometer fibers onto asupport layer, the support layer optionally comprising microfibers, soas to form a population of sub-micrometer fibers on the support layer orsubstrate. The method may comprise a step wherein the support layer,which optionally comprises polymeric microfibers, is passed through afiber stream of sub-micrometer fibers having a median fiber diameter ofno greater than 1 micrometer (μm). While passing through the fiberstream, sub-micrometer fibers may be deposited onto the support layer soas to be temporarily or permanently bonded to the support layer. Whenthe fibers are deposited onto the support layer, the fibers mayoptionally bond to one another, and may further harden while on thesupport layer.

A number of processes may be used to produce and deposit sub-micrometerfibers, including, but not limited to melt blowing, melt spinning, orcombination thereof. Particularly suitable processes include, but arenot limited to, processes disclosed in U.S. Pat. No. 3,874,886 (Levecqueet al.), U.S. Pat. No. 4,363,646 (Torobin), U.S. Pat. No. 4,536,361(Torobin), U.S. Pat. No. 5,227,107 (Dickenson et al.), U.S. Pat. No.6,183,670 (Torobin), U.S. Pat. No. 6,743,273 (Chung et al.), U.S. Pat.No. 6,800,226 (Gerking), and DE 19929709 C2 (Gerking), the entiredisclosures of which are incorporated herein by reference.

Suitable processes for forming sub-micrometer fibers also includeelectrospinning processes, for example, those processes described inU.S. Pat. No. 1,975,504 (Formhals), the entire disclosures of which areincorporated herein by reference. Other suitable processes for formingsub-micrometer fibers are described in U.S. Pat. No. 6,114,017(Fabbricante et al.); U.S. Pat. No. 6,382,526 B1 (Reneker et al.); andU.S. Pat. No. 6,861,025 B2 (Erickson et al.), the entire disclosures ofwhich are incorporated herein by reference.

The methods of making nonwoven fibrous webs may be used to form asub-micrometer fiber component containing fibers formed from any of theabove-mentioned composites. Typically, the sub-micrometer fiber formingmethod step involves melt extruding a thermoformable material at a meltextrusion temperature ranging from about 130° C. to about 350° C. A dieassembly and/or coaxial nozzle assembly (see, for example, the Torobinprocess referenced above) comprises a population of spinnerets and/orcoaxial nozzles through which molten thermoformable material isextruded. In one exemplary embodiment, the coaxial nozzle assemblycomprises a population of coaxial nozzles formed into an array so as toextrude multiple streams of fibers onto a support layer or substrate.See, for example, U.S. Pat. No. 4,536,361 (FIG. 2) and U.S. Pat. No.6,183,670 (FIGS. 1-2).

A number of processes may be used to produce and deposit microfibers,including, but not limited to, melt blowing, melt spinning, filamentextrusion, plexifilament formation, spunbonding, wet spinning, dryspinning, or a combination thereof. Suitable processes for formingmicrofibers are described in U.S. Pat. No. 6,315,806 (Torobin); U.S.Pat. No. 6,114,017 (Fabbricante et al.); U.S. Pat. No. 6,382,526 B1(Reneker et al.); and U.S. Pat. No. 6,861,025 B2 (Erickson et al.).Alternatively, a population of microfibers may be formed or converted tostaple fibers and combined with a population of sub-micrometer fibersusing, for example, using a process as described in U.S. Pat. No.4,118,531 (Hauser), the entire disclosure of which is incorporatedherein by reference. In certain exemplary embodiments, the population ofmicrofibers comprises a web of bonded microfibers, wherein bonding isachieved using thermal bonding, adhesive bonding, powdered binder,hydroentangling, needlepunching, calendering, or a combination thereof,as described below.

A variety of equipment and techniques are known in the art for meltprocessing polymeric fine fibers. Such equipment and techniques aredisclosed, for example, in U.S. Pat. No. 3,565,985 (Schrenk et al.);U.S. Pat. No. 5,427,842 (Bland et. al.); U.S. Pat. Nos. 5,589,122 and5,599,602 (Leonard); and U.S. Pat. No. 5,660,922 (Henidge et al.).Examples of melt processing equipment include, but are not limited to,extruders (single and twin screw), Banbury mixers, and Brabenderextruders for melt processing the inventive fine fibers.

The (BMF) meltblowing process is one particular exemplary method offorming a nonwoven web where a polymer fluid, either molten or as asolution, is extruded through one or more rows of holes then impinged bya high velocity gas jet. The gas jet, typically heated air, entrains anddraws the polymer fluid and helps to solidify the polymer into a fiber.The solid fiber is then collected on solid or porous surface as anonwoven web. This process is described by Van Wente in “SuperfineThermoplastic Fibers”, Industrial Engineering Chemistry, vol. 48, pp.1342-1346. An improved version of the meltblowing process is describedby Buntin et al. as described in U.S. Pat. No. 3,849,241, andincorporated by reference herein in its entirety.

Depending on the condition of the fibers, some bonding may occur betweenthe fibers during collection. However, further bonding between thefibers in the collected web can be needed to provide a matrix of desiredcoherency, making the web more handleable and better able to hold thefibers within the matrix (“bonding” fibers means adhering the fiberstogether firmly, so they generally do not separate when the web issubjected to normal handling).

Conventional bonding techniques using heat and pressure applied in apoint-bonding process or by smooth calender rolls can be used, thoughsuch processes may cause undesired deformation of fibers or compactionof the web. Another technique for bonding the fibers is taught in U.S.Patent Application Publication No. 2008/0038976. Apparatus forperforming this technique is illustrated in FIGS. 1, 5 and 6 of thedrawings. In brief summary, as applied to the present disclosure, thispreferred technique involves subjecting the collected web to acontrolled heating and quenching operation that includes a) forcefullypassing through the web a gaseous stream heated to a temperaturesufficient to soften the fibers sufficiently to cause the fibers to bondtogether at points of fiber intersection (e.g., at sufficient points ofintersection to form a coherent or bonded matrix), the heated streambeing applied for a discrete time too short to wholly melt the fibers,and b) immediately forcefully passing through the web a gaseous streamat a temperature at least 50° C. no greater than the heated stream toquench the fibers (as defined in the above-mentioned U.S. PatentApplication Publication No. 2008/0038976, “forcefully” means that aforce in addition to normal room pressure is applied to the gaseousstream to propel the stream through the web; “immediately” means as partof the same operation, i.e., without an intervening time of storage asoccurs when a web is wound into a roll before the next processing step).As a shorthand term this technique is described as the quenched flowheating technique, and the apparatus as a quenched flow heater.

Treatment of the collected web at such a temperature is found to causethe microfibers to become morphologically refined, which is understoodas follows (we do not wish to be bound by statements herein of our“understanding,” which generally involve some theoreticalconsiderations). As to the amorphous-characterized phase, the amount ofmolecular material of the phase susceptible to undesirable(softening-impeding) crystal growth is not as great as it was beforetreatment. The amorphous-characterized phase is understood to haveexperienced a kind of cleansing or reduction of molecular structure thatwould lead to undesirable increases in crystallinity in conventionaluntreated fibers during a thermal bonding operation. Treated fibers ofcertain exemplary embodiments of the present invention may be capable ofa kind of “repeatable softening,” meaning that the fibers, andparticularly the amorphous-characterized phase of the fibers, willundergo to some degree a repeated cycle of softening and resolidifyingas the fibers are exposed to a cycle of raised and lowered temperaturewithin a temperature region lower than that which would cause melting ofthe whole fiber.

In practical terms, repeatable softening is indicated when a treated web(which already generally exhibits a useful bonding as a result of theheating and quenching treatment) can be heated to cause furtherautogenous bonding of the fibers. The cycling of softening andresolidifying may not continue indefinitely, but it is generallysufficient that the fibers may be initially bonded by exposure to heat,e.g., during a heat treatment according to certain exemplary embodimentsof the present invention, and later heated again to cause re-softeningand further bonding, or, if desired, other operations, such ascalendering or re-shaping. For example, a web may be calendered to asmooth surface or given a nonplanar shape, e.g., molded into a facemask, taking advantage of the improved bonding capability of the fibers(though in such cases the bonding is not limited to autogenous bonding).

The diameters of the fibers can be tailored to provide neededfiltration, acoustic absorption, and other properties. For example itmay be desirable for the microfibers to have a median diameter of 5 to50 micrometers (μm) and the sub-micrometer fibers to have a mediandiameter from 0.1 μm to no greater than 1 μm, for example, 0.9 μm.Preferably the microfibers have a median diameter between 5 μm and 50μm, whereas the sub-micrometer fibers preferably have a median diameterof 0.5 μm to no greater than 1 μm, for example, 0.9 μm.

Various procedures are also available for electrically charging adimensionally stable nonwoven fibrous web to enhance its filtrationcapacity: see e.g., U.S. Pat. No. 5,496,507 (Angadjivand).

In addition to the foregoing methods of making a nonwoven fibrous web,one or more of the following process steps may be carried out on the webonce formed:

(1) advancing the nonwoven fibrous web along a process pathway towardfurther processing operations;

(2) bringing one or more additional layers into contact with an outersurface of the nonwoven web;

(3) calendering the nonwoven fibrous web;

(4) coating the nonwoven fibrous web with a surface treatment or othercomposition (e.g., a fire retardant composition, an adhesivecomposition, or a print layer);

(5) attaching the nonwoven fibrous web to a cardboard or plastic tube;

(6) winding-up the nonwoven fibrous web in the form of a roll;

(7) slitting the nonwoven fibrous web to form two or more slit rollsand/or a plurality of slit sheets;

(8) placing the nonwoven fibrous web in a mold and molding the nonwovenfibrous web into a new shape;

(9) applying a release liner over an exposed optional pressure-sensitiveadhesive layer, when present; and

(10) attaching the nonwoven fibrous web to another substrate via anadhesive or any other attachment device including, but not limited to,clips, brackets, bolts/screws, nails, and straps.

Articles Formed from Nonwoven Fibrous Webs

The present disclosure is also directed to methods of using the nonwovenfibrous webs of the present disclosure in a variety of applications. Ina further aspect, the disclosure relates to an article comprising anonwoven fibrous web according to the present disclosure. In exemplaryembodiments, the article may be used as a gas filtration article, aliquid filtration article, a sound absorption article, a thermalinsulation article, a surface cleaning article (e.g., wipe), a cellulargrowth support article, a drug delivery article, a personal hygienearticle, a dental hygiene article, a surgical drape, a surgicalequipment isolation drape, a medical isolation drape, a surgical gown, amedical gown, healthcare patient gowns and attire, an apron or otherapparel, a sterilization wrap, a wipe, agricultural fabrics, foodpackaging, packaging, a tape backing, or a wound dressing article.

In certain embodiments, a nonwoven fibrous web of the present disclosuremay be advantageous in gas filtration applications. Gas filters such asthis may be particularly useful in personal protection respirators;heating, ventilation and air conditioning (HVAC) filters; automotive airfilters (e.g., automotive engine air cleaners, automotive exhaust gasfiltration, automotive passenger compartment air filtration); and othergas-particulate filtration applications.

Various embodiments of the presently disclosed invention also providesuseful articles made from fabrics and webs of fine fibers includingmedical drapes, medical gowns, aprons, filter media, industrial wipesand personal care and home care products such as diapers, facial tissue,facial wipes, wet wipes, dry wipes, disposable absorbent articles andgarments such as disposable and reusable garments including infantdiapers or training pants, adult incontinence products, feminine hygieneproducts such as sanitary napkins and panty liners and the like. Thefibers and nonwoven webs described herein may also may be useful forproducing clothing, thermal insulation for garments such as coats,jackets, gloves, cold weather pants, boots, and the like as well asacoustical insulation.

Other medical devices that may be made, in whole or in part, of thefibers and/or nonwoven webs described herein include: surgical mesh,slings, orthopedic pins (including bone filling augmentation material),adhesion barriers, stents, guided tissue repair/regeneration devices,articular cartilage repair devices, nerve guides, tendon repair devices,atrial septal defect repair devices, pericardial patches, bulking andfilling agents, vein valves, bone marrow scaffolds, meniscusregeneration devices, ligament and tendon grafts, ocular cell implants,spinal fusion cages, skin substitutes, dural substitutes, bone graftsubstitutes, bone dowels, and hemostats.

It is believed that the nonwoven webs described herein can be sterilizedby gamma radiation or electron beam without significant loss of physicalstrength (tensile strength for a 1 mil thick film does not decrease bymore than 20% and preferably by not more than 10% after exposure to 2.5Mrad gamma radiation from a cobalt gamma radiation source and aged at23° C.-25° C. for 7 days). Similarly, it is expected that the nonwovenmaterials described herein can be sterilized by exposure to electronbeam irradiation. Alternatively, the nonwoven webs described herein canbe sterilized by gas or vapor phase antimicrobial agents such asethylene oxide, hydrogen peroxide plasma, peracetic acid, ozone, andsimilar alkylating and/or oxidizing agents.

EXAMPLES

The invention will be described in greater detail by way of specificexamples. The following examples are offered for illustrative purposes,and are not intended to limit the invention in any manner. Those ofskill in the art will readily recognize a variety of non-criticalparameters which can be changed or modified to yield essentially thesame results.

Overview

Since the breakout of COVID-19, there has been an increased interest inPersonal Protective Equipment (PPE) such as face masks. At times, thesematerials have been in critical short supply. The currently availablecloth face masks do not protect the wearer but mitigate the possibilityof spreading the virus. N95 masks do protect the wearer but consistentsupply has been problematic in the midst of the pandemic. In addition,existing masks are generally not very comfortable and absorb moisturefrom breath.

We propose to develop a new technology for face mask manufacturing basedon polymer (polyisobutylene-based) fiber mats. A polyisobutylene-basedpolymer (SIBS) forms the matrix of the drug eluting coating on coronarystents sold under the tradename TAXUS. These stents have a long historyof clinical use; they were approved by the FDA for clinical use in 2004and have since been implanted into over 6 million people. As describedherein, SIBS can be combined with a filler (an antimicrobial filler) andprocessed into a nonwoven fiber mat using a suitable fiber-formingtechnology. For example, a polyisobutylene thermoplastic elastomer wascombined with a zinc oxide filler and electrospun to formwater-repellent rubbery mats. These mats were not cytotoxic and inprinciple could exhibit antimicrobial activity resulting from the ZnOloaded in the polymer fibers. These mats could be fashioned intofacemasks and other PPE such as gowns etc.

Background

Electrospinning is a versatile and unique technique to produce fibers inthe range of microns to nanometers from polymer solutions usingelectrostatic forces [1]. These fibers with smaller pores and highersurface area have great potential in the biomedical industry because ofthe ease of fabrication of fibers from a wide array ofpolymers—biodegradable, non-degradable, synthetic, natural, or theirblends. Some synthetic biocompatible polymers can be easily spun intofiber mats to make stretchable wound dressings, flexible scaffolds forcell growth and tissue engineering, and implantable membranes/coatingswith the capability of controlled drug delivery.

Elastomers, which have the elasticity of natural rubber, are widely usedin industry due to their durable and tough nature. Since elastomers havelow glass transition temperature, it is very difficult to electrospinthem into stable nanofibers. Also, the electrospun fibers on thecollector may fuse quickly into large fibers or sometimes even acontinuous film [2]. Electrospinning of thermoplastic elastomers (TPEs)is easier since they can be processed as plastics but exhibitelastomeric properties. Various TPEs have been electrospun in the lasttwo decades. Sencadas et al. studied the electrospinning ofpoly(styrene-b-butadiene-b-styrene) (SBS) TPE into fiber membranes andshowed that the membranes were hydrophobic with a contact angle of 132°and the tensile strength was 0.525 MPa with 345% elongation at break[3]. These authors also explained that the mechanical strength of themat was lower than that of the bulk material (SBS) because of the higherporosity of the fibrous membrane. Since the fibers were not orderlyarranged in the nonwoven membrane, and only a small portion of thefibers resisted to the applied mechanical loading which caused lesschain entanglements per unit mass of the porous membrane. Theelectrospinning of poly(styrene-b-isoprene-b-styrene) TPEs wasdemonstrated by Supaphol et al. and they produced fibers in the range of2.7-16 μm [4]. Although electrospinning can produce ultrafine fibers,but their fibers were uncharacteristically large. They theorized thatTPE molecules usually stretch while flowing through a restricted channelof the nozzle and after leaving recoiling occurs very fast which couldprevent Coulombic stretching to decrease the fiber diameter. Similarly,larger fiber diameter (6 μm) was also found forpoly(styrene-b-(ethylene-co-1-butene)-b-styrene) triblock copolymer(SEBS) fibers [5].

We have focused on polyisobutylene (PIB)-based TPEs because of theexcellent bioinertness and biostability of PIB. A linearpoly(styrene-b-isobutylene-b-styrene) triblock copolymer (L_SIBS), a TPEis used in clinical practice as a polymer matrix of a drug-elutingcoating on the TAXUS coronary stent [6]. Over 6 million patients havebenefited from this device, emphasizing the significance of PIB-basedbiomaterials. Due to the unique low permeability of L_SIBS, sustaineddrug delivery is achieved, but only approximately 10% of theencapsulated drug, Taxol, elutes from the coating, which is therapeuticfor this application. After the success of L_SIBS, we developed anotherTPE, Arbomatrix, comprising a branched (arborescent or dendritic) PIBcore and end blocks of poly(p-methylstyrene) (PMS) [7,8]. Arbomatrix andits carbon composite was also shown to be bioinert in a rabbit model[9]. ElectroNanospray™, a technology of generating high velocity sprayof nanoparticles, was used to coat several batches of Arbomatrixpolymers loaded with Dexamethasone (DXM), a model drug, onto coronarystents. This particulate coating did not have an initial burst releasebut exhibited slow continuous release over time (20-40% release in 28days) [10]. For biomedical applications requiring more release, wetheorized that encapsulating drugs into electrospun fiber mats wouldprovide high surface area to volume ratio to release more drug. However,Liu et al. [11] reported that neat L_SIBS could not be electrospun,attributing this to the non-conductivity of the polymer solution. Wereported conditions under which we electrospun neat L_SIBS andArbomatrix onto aluminum stubs [12]. Subsequently we developed a newmethod that produced self-supporting fiber mats by electrospinning froma mixture of Arbomatrix and low molecular weight poly(ethylene glycol),PEG. The ratio of Arbomatrix to PEG was chosen to be 80/20 wt/wt basedon scouting experiments. The fiber mats were highly water-repellent,with Water Contact Angles (WCA)>120°. We successfully encapsulated amodel drug, Zafirlukast, into the fibers, and demonstrated greater than90% release [13]. Although electrospinning can produce ultrafine fibers,the mean fiber size for Zafirlukast-loaded Arbomatrix/PEG fibers waslarger (4.197 (±0.580) μm). However, this system showed higher doses andslower release rates than a recent study using poly(lactic-co-glycolicacid) polymer coating with a similar drug for reducing the capsularcontracture (an inflammatory response around silicone rubber breastprostheses) in vivo [14]. We also reported the electrospinning of a newlinear PIB-based TPE, poly(alloocimene-b-isobutylene-b-alloocimene) orMBA for short. It is also a triblock copolymer like L_SIBS but containspolyalloocimene hard blocks instead of polystyrene. It is synthesized bythe carbocationic copolymerization of isobutylene (IB) with alloocimene(Allo) [15, 16]. AIBA is easier to synthesize than Arbomatrix [8] and ithas higher tensile strength (15 MPa and 600% elongation at break) thanArbomatrix (5.6 MPa and 290% elongation at break). Electrospinning ofnon-polar and highly non-conductive materials such as AIBA is achallenge, because the process employs high voltage to electricallycharge the polymer jets to produce ultrafine fibers [1]. Therefore, thepolymer was mixed with PEG to enhance the electrical conductivity inorder to produce self-supporting fiber mats. MBA is a candidate for drugdelivery systems. Although MBA is a highly hydrophobic material that isnon-polar and therefore has high electric resistivity, fiber mats with aproper morphology were still successfully obtained. We found that PEGwas fully embedded into the electrospun fibers. The tensile strengthmeasured on microdumbbells was 2.7 MPa at 537% elongation that iscomparable to that of soft human tissues. These rubbery fiber mats werealso found to be highly hydrophobic and cell culture studies showedtheir non-cytotoxicity [17]. Based on these favorable properties, thesefiber mats showed a great promise for tissue scaffold and drug deliveryapplications.

Fiber Mats

Electrospun fiber mats were formed for antibacterial and antiviral PPEapplications. Specifically, these mats could be used to produce N95equivalent masks with better sealing, no water absorption and bettercomfort. Two basic proprietary formulations were used. Both included apolyisobutylene thermoplastic elastomer. The first (“white”) formulationincluded a zinc oxide filler. The second (“black”) formulation includeda carbon filler (carbon black). Zinc oxide itself has wound healing andantibacterial properties so it is advantageous for wound healingapplications. It also imparts UV stability to the mats. The addition ofcarbon increases conductivity and biocompatibility [9]. It also makesthe mats black (which may be aesthetically desirable in a certainsituations).

Conventional N95 masks have high filtration efficiency but are thickerthan surgical masks and rather uncomfortable for long-term use in dailylife. N95 masks can impede breathing, and users experience problems dueto the increase in temperature and humidity between the face and themask. Masks fabricated from the fiber mats prepared herein can addressthese problems. Conventional face masks include a thin layer ofelectrospun or meltblown poly(vinylidene fluoride) (PVDF) orpolycaprolactone (PCL or nylon) (basis weight of <10 g/square meter).These fiber mat filters are claimed to have a 99.9% barrier efficiencyagainst viruses, but the mats are not self-supporting, so they must beincorporated into a self-supporting structure. Typically, this meansthat one or more layers of this material are combined with one or morethicker supporting layers to form a multilayer which has the structuralintegrity to be fabricated into a mask. In contrast, these

COVID-19 is about 0.125 micron in size, but often travels in biologicalaerosols from coughing or sneezing that are 0.5-3 micron in size andprefer hydrophilic surfaces. The fiber mats prepared herein aresuperhydrophobic, like lotus leaves from which water droplets roll off,can be made with pores smaller than COVID-19 virus particles, and areself-supporting at 100 g/m² or more. The stretchable mats can beattached to rubber frames, creating a tight fit around the nose andmouth. They can be sterilized by several methods, including ethyleneoxide, low pressure plasma treatment or chlorodioxide. If desired, theycan also be recycled by simply dissolving them and re-spinning into anew fiber mat.

Example Fiber Mats

A linear poly(styrene-b-isobutylene-b-styrene) triblock copolymer(L_SIBS), sold under the tradename SIBSTAR, was obtained from Kaneka Co.of Japan. Butyl rubber (IIR) was obtained from ExxonMobil (commerciallyavailable under the tradename ExxonMobil 268).

A base formulation was prepared containing L_SIBS/IIR 50/50 by weightwas prepared. Varying concentrations of filler (ranging from 5% to 20%by weight) were then added to this blend to form composites for use infiber formation. For initial proof of principle studies, a compositecontaining 5% by weight zinc oxide (Formulation 1) and a compositecontaining 5% by weight carbon black (Formulation 2) were prepared.

A series of 24 different fiber mats were prepared by electrospinningeither Formulation 1 (47.5% by weight L_SIBS/47.5% by weight IIR/5% byweight ZnO) or Formulation 2 (47.5% by weight L_SIBS/47.5% by weightIIR/5% by weight carbon black) to form nonwoven webs having variousbasis weights ranging from 13.8 g/m² to 121.8 g/m². The basis weight ofthe Formulation 1 samples were as follows: 24.5; 84.0; 67.9; 85.6; 60.4;24.9; 24.5; 25.8; 38.7; 35.5; 16.6; 14.8; 13.8; and 15.4 g/m². The basisweight of the Formulation 2 samples were as follows: 121.8; 51.8; 26.4;21.8; 42.2; 42.6; 42.3; 42.4; 82.8; and 101.2 g/m².

Fiber diameter was kept as a constant to evaluate the effect of webthickness on filtration efficiency. Fiber diameter was evaluated withoptical microscopy and it was concluded that the mean fiber diameter isaround 1 micrometer in all webs. Material samples were collected on a PPsubstrate.

FIGS. 2A and 3A show a photograph of example nonwoven webs prepared byelectrospinning Formulation 2 and Formulation 1, respectively. As shownin FIGS. 2B and 3B, these nonwovens include a plurality randomlyoriented individual fine fibers interlaid to produce self-supportingcohesive nonwoven webs.

Five samples with different basis weights were selected, and thefiltration efficiency and corresponding pressure drop were evaluatedusing standard methods set forth in the U.S. NIOSH (National Institutefor Occupational Safety and Health) N95 Filtering Facepiece Respirator(FFR) certification method. The filtration efficiency was measured withNaCl particles ranging from 20 nm-450 nm. Filtration efficiency ispresented both on average and also at 300 nm particles only.

TABLE 1 Summary of properties of example nonwoven webs. Basis WeightPressure Eff % Example Filler (g/m²) Drop (Pa) Eff % (300 nm) 1 carbon26.4 26 42.2% 20.3% black 2 carbon 42.6 42 45.6% 25.2% black 3 ZnO 13.845 54.6% 34.6% 4 ZnO 16.6 54 52.4% 31.7% 5 ZnO 35.5 121 67.1% 51.4%

FIG. 4 shows a plot of the filtration efficiency as a function ofpressure drop for example webs 1-5. As shown in FIG. 4 , filtrationefficiency increased as pressure drop increased, suggesting that websmeeting the N95 standard could be generated by increasing the basisweight of the webs.

FIG. 5 shows an example water contact measurement performed on thesurface of an example web. As shown in FIG. 5 , these example websexhibited water contact angles of greater that 130°, indicating thatthese webs are strongly hydrophobic. This suggests that face masksfabricated from these webs would be water repellant, improving comfortfor wearers—in particular, for those wearing masks for long periods oftime, for those wearing masks in high humidity environments, for thosewearing masks when breathing heavily, or any combination thereof.

Example webs having basis weights of 100 g/m² or more were found to beself-supporting. As shown in FIG. 6 , such example webs could beformulated into face masks without needed to be combined with additionalnonwoven layer (e.g., there was no need for an outer and/or innerspunbond layer to support the nonwoven web).

In a further proof of principle studies, formulations containing higherfiller loadings were prepared and electrospun as described above to formwebs of varying basis weight (see Table 2 below). These formulationsalso generated high quality self-supporting nonwoven fibrous webs.

TABLE 2 Additional nonwoven webs prepared using higher filler loadings.Example Filler Basis Weight (g/m²) 6 10% ZnO 295.5 7 10% ZnO 203.8 8 20%ZnO 107.0 9 20% ZnO 105.0 10 20% ZnO 113.0 11 20% ZnO 90.0

REFERENCES

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The compositions, devices, and methods of the appended claims are notlimited in scope by the specific compositions, devices, and methodsdescribed herein, which are intended as illustrations of a few aspectsof the claims. Any compositions, devices, and methods that arefunctionally equivalent are intended to fall within the scope of theclaims. Various modifications of the compositions, devices, and methodsin addition to those shown and described herein are intended to fallwithin the scope of the appended claims. Further, while only certainrepresentative compositions, devices, and methods steps disclosed hereinare specifically described, other combinations of the compositions,devices, and methods steps also are intended to fall within the scope ofthe appended claims, even if not specifically recited. Thus, acombination of steps, elements, components, or constituents may beexplicitly mentioned herein or less, however, other combinations ofsteps, elements, components, and constituents are included, even thoughnot explicitly stated.

The term “comprising” and variations thereof as used herein is usedsynonymously with the term “including” and variations thereof and areopen, non-limiting terms. Although the terms “comprising” and“including” have been used herein to describe various embodiments, theterms “consisting essentially of” and “consisting of” can be used inplace of “comprising” and “including” to provide for more specificembodiments of the invention and are also disclosed. Other than wherenoted, all numbers expressing geometries, dimensions, and so forth usedin the specification and claims are to be understood at the very least,and not as an attempt to limit the application of the doctrine ofequivalents to the scope of the claims, to be construed in light of thenumber of significant digits and ordinary rounding approaches.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meanings as commonly understood by one of skill in the artto which the disclosed invention belongs. Publications cited herein andthe materials for which they are cited are specifically incorporated byreference.

1. A nonwoven fibrous web comprising a population of fibers, wherein thefibers are formed from a composite that comprises: (i) a thermoplasticelastomeric polymer (TPE) component; (ii) a soft elastomeric polymercomponent that at ambient temperatures is above its glass transitiontemperature; and (iii) optionally a filler.
 2. The web of claim 1,wherein the TPE component comprises a polyisobutylene-based TPE.
 3. Theweb of claim 1, wherein the TPE component comprises triblock copolymerhaving at least one elastomeric polyisobutylene block.
 4. The web ofclaim 1, wherein the TPE component comprisespolystyrene-polyisobutylene-polystyrene (SIBS).
 5. The web of claim 1,wherein the TPE component comprisespoly(alloocimene-b-isobutylene-b-alloocimene).
 6. The web of claim 1,wherein the TPE component has a structure selected from the groupconsisting of linear, star, arborescent, comb, brush, centipede,hyperbranched, and dendritic.
 7. The web of claim 1, wherein the softelastomeric polymer component is selected from the group consisting ofpolyisobutylene, polyisobutylene-isoprene copolymers,polyisobutylene-styrene copolymers, polyisobutylene-alkyl styrenecopolymers, halogenated polyisobutylene-alkyl styrene terpolymers, andcombinations thereof.
 8. (canceled)
 9. The web of claim 1, wherein thesoft elastomeric polymer component has a structure selected from thegroup consisting of linear, star, arborescent, comb, brush, centipede,hyperbranched, and dendritic.
 10. The web of claim 1, wherein the TPE ispresent in an amount from about 10% to about 90% by weight of thecomposite, and wherein the soft elastomeric polymer component is presentin an amount from about 90 to about 10% by weight of the composite,based on the total weight of the composite.
 11. (canceled)
 12. The webof claim 1, wherein the filler is present in an amount from about 2% toabout 40% by weight of the composite, such as from about 5% to about 30%by weight, based on the total weight of the composite.
 13. The web ofclaim 1, wherein the filler comprises an antimicrobial filler.
 14. Theweb of claim 1, wherein the antimicrobial filler is an inorganicmaterial that comprises one more antimicrobial metals chosen fromsilver, copper, zinc, and combinations thereof.
 15. (canceled)
 16. Theweb of claim 1, wherein the population of fibers comprises population offine fibers, a population of microfibers, a population of ultrafinemicrofibers, a population of sub-micrometer fibers, or any combinationthereof.
 17. The web of claim 1, wherein the nonwoven fibrous web isformed as a single layer.
 18. The web of claim 1, wherein the nonwovenweb is self-supporting.
 19. The web of claim 1, wherein the nonwovenfibrous web exhibits a water contact angle of at least 120°, asdetermined by goineometry.
 20. The web of claim 1, wherein the nonwovenweb has a basis weight of at least 80 g/m², such as a basis weight of atleast 100 g/m², at least 150 g/m², or at least 200 g/m².
 21. The web ofclaim 1, wherein the nonwoven web exhibits an average filtrationefficiency relative to 20 nm to 450 nm NaCl particles of at least 60%,measured using the U.S. NIOSH (National Institute for OccupationalSafety and Health) N95 Filtering Facepiece Respirator (FFR)certification method.
 22. (canceled)
 23. An article comprising anonwoven fibrous web defined by claim 1, selected from the groupconsisting of a gas filtration article, a liquid filtration article, asound absorption article, a surface cleaning article, a cellular growthsupport article, a drug delivery article, a personal hygiene article,and a wound dressing article.
 24. (canceled)
 25. A method of making afibrous nonwoven web, the method comprising: forming a plurality offibers from a composite comprising: (i) a thermoplastic elastomericpolymer (TPE) component; (ii) a soft elastomeric polymer component thatat ambient temperatures is above its glass transition temperature; and(iii) optionally a filler; and collecting at least a portion of thefibers to form a nonwoven web. 26-46. (canceled)